Aggravate monster

The aggravate monsterproperty greatly amplifies the chance that nearby sleepingmonsters will be awakened if you move near them. While you have this property, monsters can usually tell where you are even if they cannot see you. Also, abusing pets will halve their tameness instead of reducing it by one.

Gaining the property

eating any cat or dog corpse (or their less or more grown up forms), unless you are an orc or caveperson (then it is harmless)

sacrificing a former pet, if it died while it was tame ("So this is how you repay loyalty?"). If the pet went feral (peaceful or hostile) and then died, sacrificing it is okay.

eating a corpse of your own race (cannibalism), unless you are an orc or caveperson

eating a ring of aggravate monster

The effect of this type of aggravate monster is almost completely nullified by stealth.

While extrinsic aggravate monster can be eliminated by simply removing the ring, the intrinsic property is very difficult to get rid of. The only way to do so is to have a gremlin steal it from you at night or eat disenchanter corpses. However, be warned that you are likely to lose a number of good intrinsics before losing the bad one--in most cases, as long as you have stealth, it is better to just finish the game with aggravate monster.

Other forms of aggravate monster

The other form of aggravate monster wakes up all monsters on the level and has a one-fifth chance of unparalyzing paralyzed monsters on the level, with the message:

turning undead while your god is angry, while in Gehennom, or while polymorphed into undead with lawful or neutral alignment

sitting on a throne (occasionally)

failing to read a spellbook (occasionally)

Monsters can also be affected when drinking a cursed potion of invisibility or being affected by the shrieker (only with conflict or pet shrieker). When this happens (nearly always by drinking the potion of invisibility), you will be shown the monster's location and receive the messages:

"For some reason, <monster> presence is known to you." "You feel aggravated at <monster>."[2]